Various recessive mutants in corn, particularly those expressed in the endosperm (e.g., shrunken, brittle, opaque, waxy, etc.), which improve the quality of the corn in such respects as sweetness, flavor and nutritive value are often impractical for large scale commercial use. This is because they are associated with undesirable production traits such as low germination and disease susceptibility.
An example involves the use of the recessive combination sugary-shrunken 2 (su sh.sub.2) which results in so-called "ultra-sweet" corn. Although the homozygous su sh.sub.2 combination results in 100% extra sweet kernels, typically considered too sweet and lacking "corn" taste and texture, it has been suggested that a "bi-sweet" hybrid can be produced using that combination as one of the parents. As I pointed out in Maize Genetics Cooperation News Letter 49: 98-99 Apr. 15, 1975), the crossing of the double recessive su sh.sub.2 with a normal sweet corn (su Sh.sub.2) would result in seed which, when planted by the farmer, would produce a crop ear segregating for approximately 25% ultra-sweet kernels and 75% normal sweet kernels. Such a "bi-sweet" corn has high commercial potential, especially for canning.
The drawback to such a system is that the su sh.sub.2 combination has an uneconomically low germination rate (in the neighborhood of 10%). Part of this problem may be overcome by using a normal sweet corn (having normal germination) as one of the parents (preferably the seed parent) in the final cross to produce the "bi-sweet" hybrid discussed above. However, the homozygous su sh.sub.2 parent seed remains defective from a germination standpoint, requiring either costly nurturing or an uneconomical 10-fold increase in the amount of seed required to grow the requisite number of parent plants.
Accordingly, there exists a need to overcome the expression of undesirable production traits which are associated with desirable traits in corn.